CN1289892C - Structure layer thickness acquisition method for multiquantum trap infrared detection material - Google Patents

Abstract

The present invention relates to an acquisition method for the structure layer thickness of the infrared detection material of multi-quantum traps. In the method, the conventional transmission spectrum measurement is adopted; measuring data and a double-layer approximate model are fitted for acquiring the actual thickness parameter of an upper electrode layer and a multi-quantum trap area in the infrared detection material of multi-quantum traps. Consequently, a necessary and actual material structure parameter is supplied to the preparation technology of subsequent devices; simultaneously, an Al constituent parameter in a barrier layer in the multi-quantum trap area can be acquired. The method can also supply a reference basis to the parameter correction of the growth process of the material.

Description

The structure bed thickness acquisition methods of Multiple Quantum Well infrared acquisition material

Technical field:

The present invention relates to a kind of multiple quantum well infrared detector material structure layer thickness and transmitted spectrum measures, specifically, be about by to the measurement of multiple quantum well infrared detector material transmitted spectrum and the application of particular module, directly obtain the method for material upper electrode layer, Multiple Quantum Well zone thickness parameter.

Background technology:

Along with the demand of infrared eye in field such as military, civilian, its material growth, device preparation have received very big concern.For example, the infrared semiconductor material that GaAs/AlGaAs two classes are important, compare with the HgCdTe material, though the GaAs/AlGaAs multiple quantum well infrared detector exists the absorption coefficient of light little, the shortcoming that carrier lifetime is short, but, growth of GaAs material and technical maturity, make repeatability easily, the large tracts of land array (FPA) of good uniformity, simultaneously, its manufacturing cost is lower, device performance is stable, and suitable large-scale production, and the AlGaAs/GaAs Multiple Quantum Well also can be formed in the detector of any infrared band work in principle, therefore, because the infrared eye by atmospheric window 8～12 mu m ranges has important application prospects at the space remote sensing technical elements in recent years, this just makes that the main developing direction of AlGaAs/GaAs multiple quantum well infrared detector (Quantum Well Infrared Photodetector QWIP) is the long wave device that is operated in 8～14 mu m ranges, so more causes people's extensive interest.

The development of molecular beam epitaxy technique, adopt the quantum effect infrared eye of manual control crystal structure to attract much attention as infrared eye of future generation, a new way that realizes 8～14 μ m infrared eyes has been created in the research and development of the GaAs/GaAlAs multiple quantum well infrared detector of development at present, and, it has unique advantage, the irreplaceable effect of other material of performance in making some high-performance detector and integrated optoelectronic circuit.Though employing molecular beam epitaxy technique, in the material growth course, can monitor extension growth for Thin Film speed by refletcion high-energy electron diffraction (RHEED) technology, but, growth rate can produce drift in the material whole growth process, make the thickness of the actual growth of material can produce deviation, this has brought difficulty for the flow technology in later stage.The structural parameters that people adopt conventional secondary ion mass spectrum method and step instrument method to wait control material usually, but these methods all need sample is carried out destructive processing, and can not be used through material after such processing, so the real sample that is used to the device preparation can't obtain its dependency structure parameter again.Any for this reason harmless detection method is determined the concrete parameter in the QWIP device technology, and then is guaranteed that the controllability of technological process is of great use.

Fig. 1 has provided GaAs/AlGaAs QWIP material typical structure synoptic diagram, is followed successively by upper electrode layer, multiquantum well region, lower electrode layer and cushion and substrate from sample surfaces.In the device preparation process, need photoetching and erode to lower electrode layer, know that upper electrode layer and the total thickness parameter of multiquantum well region seem extremely important in each sheet material; Simultaneously, for n type quantum trap infrared detector, owing to be subjected to the restriction of quantum selection rule, necessary working medium or metal coupling grating, could absorption be arranged to normal incident light, usually adopt in upper electrode layer photoetching and erode away optical grating construction, also need to understand the thickness parameter information of upper electrode layer.After obtaining these thickness parameters, the device preparation technology parameter could strictly be determined, thereby guaranteed finishing smoothly of technological process.

Summary of the invention:

As mentioned above, based on the drift of material growth rate and to cause the actual growth thickness of material uncertain be technical matters to be solved by this invention, for this reason, the purpose of this invention is to provide a kind of easy, undamaged method of obtaining in the Multiple Quantum Well infrared acquisition material the very crucial thickness parameter of device technology, for device preparation technology provides foundation smoothly.

Technical scheme of the present invention is as follows:

According to the structure bed thickness acquisition methods of a kind of Multiple Quantum Well infrared acquisition material of the present invention, be used for the upper electrode layer of GaAs/AlGaAs Multiple Quantum Well infrared acquisition material and the measurement of multiquantum well region thickness parameter, its step comprises:

A. in the transmitted spectrum measuring system of routine, measure the transmitted spectrum of mqw material earlier;

B. electrode layer, cushion and substrate under the Multiple Quantum Well infrared acquisition material structure are considered as one and as equivalent substrate layer, and with Multiple Quantum Well zone and upper electrode layer respectively as the equivalent second layer and ground floor, this equivalence second layer and ground floor are approximately the bilayer film model on the substrate;

C. after, adopt double-deck approximate model to calculate the gross data of transmitted spectrum and carry out match, obtain the thickness parameter that manufacturing process needs with above-mentioned measure spectrum data.

Further, the measuring process of described step a comprises:

(1) at first in the light path of transmitted spectrum measuring system, reserves the enough big space of placing sample, and sample is seated in to be measured inserting in the light path on the specimen holder of device level material special use;

(2) utilizing wavelength is that 500～600nm visible light regulates light path, and the signal of measuring detector this moment is with the variation in wavelength 900～1250nm scope, and the result of measurement is as the background signal of system;

(3) the Multiple Quantum Well sample is positioned in the light path, measures wavelength signal in 900～1250nm scope once more and obtain spectral signal with wavelength change;

(4) can obtain the transmitance of mqw material divided by background signal with wavelength change curve, i.e. transmitted spectrum with the above-mentioned spectral signal that records.

Its process of described step c comprises:

Theoretical calculation formula when (1) utilizing the transmissivity T computing formula of typical multilayer film to derive double-layer films normal incidence:

$T_t(n_i,d_i,{\mathrm{\λ}}_i)T=\frac{n_{k-1}}{n_0}\frac{{\left(t_0{t}_1{t}_{2}K{t}_k\right)}^2}{{\mathrm{\μ}}_{11}{\·\mathrm{\μ}}_{11}^{*}};$

(2) the upper electrode layer thickness d 10 multiquantum well region thickness d 20 of the QWIP structure parameter that forms to grow and the refractive index n of multiquantum well region by the material designing requirement _QWOBe initial value, and they made random variation, make to reach best identical between Theoretical Calculation and the experimental result:

$\mathrm{FX}=\underset{i}{\mathrm{\Σ}}{(T_e\left({\mathrm{\λ}}_i\right)-T_t(n_i,d_i,{\mathrm{\λ}}_i))}^2,$ And export final fitting parameter d1, d2 and n at last _QW,

T in the formula _e(λ _i) and T _t(n _i, d _i, λ _i) represent a certain wavelength place transmissivity experiment measuring and Theoretical Calculation result respectively.

The equivalent refractive index of described quantum well layer passes through relational expression: n by the refractive index decision of wherein potential barrier AlxGal-xAs _QW=xn _AlAs+ (1-x) n _GaAsAnd try to achieve the refractive index of quantum well region from the Al component x value that semiconductor material parameter handbook checks in quantum well region.

Great advantage of the present invention is:

(1) spectral measurement has noncontact, undamaged advantage, is very suitable for definite structural sheet basic parameter that will be used for the QWIP material of device preparation;

(2) utilize the model that proposes among the present invention, the material growth actual (real) thickness of paying special attention in device preparation technology parameter can be provided quickly and accurately;

Light path need not to readjust after sample was put into when (3) carrying out the transmitted spectrum measurement, had guaranteed convenience and the reliability measured, was suitable for measuring routinely.

Description of drawings:

A kind of GaAs/AlGaAs multiple quantum well infrared detector material typical structure synoptic diagram that Fig. 1 will measure for the present invention;

Fig. 2 is a transmitted spectrum experiment measuring system schematic used in the present invention;

Fig. 3 is the experimental result (dotted line) of several embodiment correspondences of using the inventive method and doing and the comparison synoptic diagram of fitting result (solid line).

Embodiment:

Provide better embodiment of the present invention according to Fig. 1～Fig. 3 below, and method of the present invention be described in further detail in conjunction with this embodiment:

The embodiment specimen in use is the QWIP material of growing in the molecular beam epitaxy system, and material number is QWIP1018, and GaAs (001) is as substrate, AlGaAs layer Al component value x=0.11 in the multiquantum well region.

As shown in Figure 1, the QWIP material 20 that present embodiment is used, it is made up of 104 layer films altogether,, is followed successively by upper electrode layer 21, multiple quantum well layer 22, lower electrode layer 23, cushion 24 and substrate 25 from top to bottom.The present invention proposes lower electrode layer 23, cushion 24 are considered as being one with substrate 25, be called equivalent substrate layer, 101 layers with the Multiple Quantum Well zone of 50 quantum wells are considered as the equivalent second layer, upper electrode layer 21 is called ground floor, so just 104 layer films on the substrate 25 is approximately the model of the bilayer film on the substrate 25.

Present embodiment adopts conventional transmission measurement system, concrete experimental provision as shown in Figure 2, wherein light source 1 is the halogen tungsten lamp of Oriel company (model is 66184); Monochromator 2 is 1/8m (model: 74000, computer control) of Oriel company; Detector 6 is the Ge detector of working and room temperature; Adopt EG﹠amp; (model: lock-in amplifier 7 5209) also carries out data acquisition by computing machine 9 to G.Concrete measuring process is:

(1) at first, sample 3 is not placed in the light path, and it is enough big that want in the space of the storing sample 3 of light path, and sample 3 is seated on the specimen holder of device level material special use simultaneously, guarantees that sample is not stain, and can carry out the device flow easily after measurement.

(2) utilize wavelength to regulate light path (light source is through shining directly in the photosensitive unit of detector 6 behind monochromator 2, chopper wheel 4 and the lens 5) for the 500-600nm visible light and the signal response of measuring detector 6 at this moment with wavelength (scope: variation 900-1250nm), the spectral results of measurement is as the background of system;

(3) Multiple Quantum Well sample 3 is put into light path (keep other element motionless), measured once more that signal obtains spectrum with wavelength change in the wavelength 900-1250nm scope;

(4) result who measures with step 3 can obtain mqw material divided by background signal transmitance with the wavelength change curve, i.e. transmitted spectrum, as shown in phantom in Figure 3.Wherein the oscillation peaks amplitude of interference fringe is 0.5%.

In the present embodiment with the refractive index n QW of the thickness d 2 of the thickness d 1 of the upper electrode layer 21 of QWIP material, quantum well layer, quantum well region as the match parameter, the transmitted spectrum that measures is carried out data fitting, wherein the equivalent refractive index of multiple quantum well layer 22 can be represented with following formula by the refractive index decision of wherein potential barrier AlxGal-xAs:

n _QW＝x·n _AlAs+(1-x)n _GaAs (1)

Wherein, nQW, nAlAs, nGaAs represent the refractive index of Multiple Quantum Well, AlAs, GaAs respectively, check near the nAlAs=2.9 1 μ m from semiconductor material parameter handbook, nGaAs=3.4, x are that barrier layer Al component (x=0.11 among the sample QWIP1018) is 3.345 according to the refractive index that formula 1 can obtain quantum well region in the Multiple Quantum Well.

Utilize the transmissivity T computing formula of typical multilayer film:

$T=\frac{n_{k+1}}{n_0}\frac{{\left(t_0{t}_1{t}_{2}K{t}_k\right)}^2}{{\mathrm{\μ}}_{11}{\·\mathrm{\μ}}_{11}^{*}}$ (light positive incident situation);

$T=\frac{n_{k+1}\cos {\mathrm{\θ}}_{k+1}}{n_0\cos {\mathrm{\θ}}_0}\frac{{\left(t_0{t}_1{t}_{2}K{t}_k\right)}^2}{{\mathrm{\μ}}_{11}{\·\mathrm{\μ}}_{11}^{*}}$ (light oblique incidence situation);

Wherein: $t_0=\frac{{2n}_0}{n_0+n_1},r_0=\frac{n_0-n_1}{n_0+n_1};t_1=\frac{{2n}_1}{n_1+n_2},r_1=\frac{n_1-n_2}{n_1+n_2};t_2=\frac{{2n}_2}{n_2+{\mathrm{<figure-callout\; id="3"\; label="n"\; filenames="C20031010924700121.png"\; state="\{\{state\}\}">n</figure-callout>}}_3},r_2=\frac{n_2-n_3}{n_2+{\mathrm{<figure-callout\; id="3"\; label="n"\; filenames="C20031010924700121.png"\; state="\{\{state\}\}">n</figure-callout>}}_3};\&CenterDot;\&CenterDot;\&CenterDot;;$ $t_k=\frac{{2n}_k}{n_k+n_{k+1}},r_k=\frac{n_k-n_{k+1}}{n_k+n_{k+1}};$ Parameter K is the number of plies sequence number of multilayer film; Parameter μ ₁₁Be plural number, μ ^* ₁₁Be μ ₁₁Conjugate complex number;

In addition, $M_0=\left[\begin{array}{cc}1& r_0\\ r_0& 1\end{array}\right],M_m=\left[\begin{array}{cc}{e}^{{\mathrm{j\&delta;}}_m}& r_m{e}^{j{\mathrm{\&delta;}}_m}\\ r_m{e}^{-j{\mathrm{\&delta;}}_m}& e^{-j{\mathrm{\&delta;}}_m}\end{array}\right],{\mathrm{\&delta;}}_m=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}{n}_m{d}_m\cos {\mathrm{\&theta;}}_m,$ M=1,2,3,4 ..., k; J is plural power exponent,

Order: $\underset{m=0}{\overset{k}{\mathrm{\&Pi;}}}{M}_m=\left[\begin{array}{cc}{\mathrm{\&mu;}}_{11}& {\mathrm{\&mu;}}_{12}\\ {\mathrm{\&mu;}}_{21}& {\mathrm{\&mu;}}_{22}\end{array}\right],$

Only relate to M for double-layer films ₀, M ₁, M ₂, the situation of its normal incidence can be derived:

$T(n_i,d_i,{\mathrm{\&lambda;}}_i)=\frac{n_{k+1}}{n_0}\frac{{\left(t_0{t}_1{t}_{2}K{t}_k\right)}^2}{{\mathrm{\&mu;}}_{11}{\&CenterDot;\mathrm{\&mu;}}_{11}^{*}}=1+r_0^2{r}_1^2+r_0^2{r}_2^2+r_1^2{r}_2^2+2(r_0{r}_1+r_0{r}_1{r}_2^2)\cos {2\mathrm{\&delta;}}_1$

$+2(r_1{r}_2+r_0^2{r}_1{r}_2)\cos {2\mathrm{\&delta;}}_2+2r_0{r}_2\cos 2({\mathrm{\&delta;}}_1+{\mathrm{\&delta;}}_2)+{2r}_0{r}_1^2{r}_2\cos 2({\mathrm{\&delta;}}_1-{\mathrm{\&delta;}}_2)---\left(2\right)$

N wherein ₀=1, be the refractive index of air; n _m, d _mRepresent the refractive index of m layer film and the geometric thickness of film respectively, n ₂=n _GaAs, n ₃=n _QW, θ ₀Be incident angle, get light positive incident situation in the experiment, i.e. θ ₀=0 °, that is to say θ _m=0 °.

In the concrete fit procedure, with QWIP structure parameter d10, d20 and the nQW that forms that grow by the material designing requirement is initial value, numerical value is 0 to 1 random number functions Ran (idum) in the appliance computer Fortran language, the refractive index n QW of parameter d 1, d2 and quantum well region is carried out at random variation, make the degree of agreement that reaches best between Theoretical Calculation and the experimental result, just make the FX value for minimum.The FX value is:

$\mathrm{FX}=\underset{i}{\mathrm{\&Sigma;}}{(T_e\left({\mathrm{\&lambda;}}_i\right)-T_t(n_i,d_i{,\mathrm{\&lambda;}}_i))}^2---\left(3\right)$

Te in the formula (λ i), Tt (ni, di, λ i) represent the result of a certain wavelength place transmissivity experiment measuring, Theoretical Calculation respectively.Export final fitting parameter d1, d2 and nQW at last, can obtain barrier layer Al component x value in the Multiple Quantum Well simultaneously by formula (1) again, table 1 has provided the result of several embodiments.Fig. 3 has provided the transmitted spectrum of match and the comparison of experimental measurements.

Table 1: the fitting parameter of several embodiments

Sample number into spectrum	Parameter	Design load	Initial value	Fitting result
					Qwip1012	d1(nm)	1750	1750	1906.1
d2(nm)	3360	3360	3722.8
				x		0.11	0.11	0.084
Qwip1016	d1(nm)	1750	1750						1863.3
				d2(nm)	3375	3375	4142.0
	x	0.11	0.11					0.085
				Qwip1017-1	d1(nm)	1750	1750		2122.4
d2(nm)	3390	3390	3724.1
					x	0.11	0.11	0.059
Qwip1017-2	d1(nm)	1750	1750						2047.0
				d2(nm)	3405	3405	4016.1
	x	0.11	0.11					0.09535
				Qwip1018	d1(nm)	1750	1750		2048.6
d2(nm)	3435	3435	3999.8
					x	0.11	0.11	0.0978

Claims (4)

1, a kind of structure bed thickness acquisition methods of Multiple Quantum Well infrared acquisition material is used for the upper electrode layer of GaAs/AlGaAs Multiple Quantum Well infrared acquisition material and the measurement of multiquantum well region thickness parameter, and its step comprises:

A. in the transmitted spectrum measuring system of routine, measure the transmitted spectrum of mqw material earlier;

B. electrode layer, cushion and substrate under the Multiple Quantum Well infrared acquisition material structure are considered as one and as equivalent substrate layer, and with Multiple Quantum Well zone and upper electrode layer respectively as the equivalent second layer and ground floor, this equivalence second layer and ground floor are approximately the bilayer film model on the substrate;

C. after, adopt double-deck approximate model to calculate the gross data of transmitted spectrum and carry out match, obtain the thickness parameter that manufacturing process needs with above-mentioned measure spectrum data.

2, the structure bed thickness acquisition methods of Multiple Quantum Well infrared acquisition material according to claim 1, it is characterized in that: the measuring process of described step a comprises:

(1) at first reserve the enough big space of placing sample in the light path of transmitted spectrum measuring system, and sample is seated on the specimen holder of device level material special use to be measuredly, sample is declined in the light path at this moment;

(2) utilizing wavelength is that 500～600nm visible light regulates light path, and the signal of measuring detector this moment is with the variation in wavelength 900～1250nm scope, and the result of measurement is as the background signal of system;

(3) the Multiple Quantum Well sample is positioned in the light path, measures wavelength signal in 900～1250nm scope once more and obtain spectral signal with wavelength change;

(4) can obtain the transmitance of mqw material divided by background signal with wavelength change curve, i.e. transmitted spectrum with the above-mentioned spectral signal that records.

3, the structure bed thickness acquisition methods of Multiple Quantum Well infrared acquisition material according to claim 1, it is characterized in that: its process of described step c comprises:

Theoretical calculation formula when (1) utilizing the transmissivity T computing formula of typical multilayer film to derive double-layer films normal incidence:

$T_t(n_i,d_i,{\mathrm{\&lambda;}}_i)T=\frac{n_{k+1}}{n_0}\frac{{\left(t_0{t}_1{t}_{2}K{t}_k\right)}^2}{{\mathrm{\&mu;}}_{11}\&CenterDot;{\mathrm{\&mu;}}_{11}^{*}};$

(2) refractive index n of upper electrode layer thickness d 10, multiquantum well region thickness d 20 and the multiquantum well region of the QWIP structure parameter that forms to grow by the material designing requirement _QWOBe initial value, and they made random variation, make to reach best identical between Theoretical Calculation and the experimental result: $\mathrm{FX}=\underset{i}{\mathrm{\&Sigma;}}(T_e\left({\mathrm{\&lambda;}}_i\right)-T_t{(n_i,d_i,{\mathrm{\&lambda;}}_i))}^2,$ And export final fitting parameter d1, d2 and n at last _QW,

T in the formula _e(λ _i) and T _t(n _i, d _i, λ _i) represent a certain wavelength place transmissivity experiment measuring and Theoretical Calculation result respectively.

4, the structure bed thickness acquisition methods of Multiple Quantum Well infrared acquisition material according to claim 3 is characterized in that: the equivalent refractive index of described quantum well layer passes through relational expression: n by the refractive index decision of wherein potential barrier AlxGa1-xAs _QW=xn _AlAs+ (1-x) n _GaAsAnd try to achieve the refractive index of quantum well region from the Al component x value that semiconductor material parameter handbook checks in quantum well region.

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